There are many requirements for lighting devices which are needed to project light in a substantially horizontal direction so that a distant observer can locate the light. A typical use would be a navigation light on a ship. These red or green lights are required on ships so that other ships will know of their location and avoid potential accidents. Navigation lights are normally constructed to provide a light beam of a specification intensity and a specification vertical beamwidth above and below the horizontal plane. Unfortunately, ships and other craft such as sailboats roll in the water beyond the vertical specification beamwidth of the lights such that the navigation lights misdirect their projected beam either upward or downward. This misdirection of light can create a substantial hazard as other ships are denied the lighting signal that can alert them to a potential accident.
For uses other than as navigation lights such as buoy lights the lighting device may be flashing. A flashing requirement intensifies the problem of misdirected light because for the light to be visible to a horizontal observer during a rolling motion the light must flash at substantially the exact time that the light is projecting light in the horizontal direction. Normally this requires the lighting device to be disposed substantially in the vertical position. If the light flashes when the projected beam is misdirected above or below the horizontal, virtually all of the light energy will miss the observer. If the light continues to flash at the time its beam is directed away from the horizontal, it can remain unseen for an unacceptable length of time. A misdirected steady light also has its visibility decreased by a rolling movement of the lighting device however, as the lighting device oscillates about the vertical it will at least, for a short period of time, direct some of its light in the direction of a horizontal observer.